A new HPLC-based assay for the measurement of fructosamine-3-kinase (FN3K) and FN3K-related protein activity in human erythrocytes.

BACKGROUND

An impact on glycation, and possibly on diabetic complications, is attributed to fructosamine-3-kinase (FN3K) and its related protein (FN3K-RP) because they degrade Amadori compounds in vivo. Little is known about individual differences in FN3K-RP activity, which might contribute to an individual risk for diabetic complications.

METHODS

An HPLC-based activity assay for FN3K-RP in erythrocytes with the substrate N-α-hippuryl-N-ε-psicosyllysine was developed. The activities of FN3K and FN3K-RP were also analysed in erythrocytes of 103 consecutive participants of a health-care survey amongst a high-risk group for diabetes. The potential associations of these activities with the subjects' health background (anthropometric data, glucose tolerance and HbA1c, blood lipids, history of metabolic diseases in the subjects and their families, and medication) were examined.

RESULTS

The interindividual variability of FN3K-RP is less pronounced than that of FN3K [60-135 vs. 2.8-12.5 mU/g haemoglobin (Hb)]. No correlations with age, sex, body weight, blood cholesterol, or plasma glucose in an oral glucose tolerance test were observed. Subjects with kidney disease had higher activity of mainly FN3K-RP [111±15 vs. 98±18 mU/g Hb, mean±standard deviations (SDs), n=16 vs. 87, p=0.009], whereas subjects whose parents or siblings had a stroke showed lower FN3K activity (6.2±1.6 vs. 7.1±1.8 mU/g Hb, mean±SD, n=24 vs. 66, p=0.040).

CONCLUSIONS

There is a likely impact of FN3K and FN3K-RP on the glycation cascade in vivo with potential positive and negative effects. The new screening method enables further studies to elucidate the function and importance of FN3K-RP.